Field of the Invention
The present invention relates generally to the field of apparatus for thermal detoxification of polluted soil and more particularly to mobile apparatus for infrared heating (retorting) of soil contaminated with hydrocarbons.
Discussion of the Prior Art
Contamination of earth (soil) by petroleum and other hydrocarbons is a common occurrence. Such contamination may, as examples, occur as a result of over-filling or damage to above-ground storage vessels, the rusting or corrosion of underground storage tanks, careless oil well drilling practices or oil wellhead blowouts, or damage to transport ships which causes spilled or leaking oil to wash ashore. The resulting contamination of the soil causes many environmental problems. The hydrocarbon materials may, for example, seep or be washed from the soil and enter drinking water supplies and/or the food chain in various ways. Also, the contaminants may be injurious to wildlife. Frequently, old abandoned sites of contamination are forgotten about and housing tracts are later built on the sites. The contaminated soil then creates numerous health problems, including increased rates of cancer, among inhabitants of the homes built in the contaminated sites.
At least in recent years, greater concern has been devoted to the short term and long term health and environmental effects of soil contamination. As a consequence, businesses are typically charged with the responsibility and cost of cleaning up ground areas contaminated due to their activities, whether or not such activities are, in fact, negligent. Also, many attempts are made to environmentally clean up contaminated areas which have long since been abandoned. A well publicized example of such clean up activities is the clean up of the Love Canal area in the United States, a chemically contaminated area which had been later developed into a residential area and which caused serious health problems to the residents.
In some instances, the soil contamination is of such a severe nature that physical removal of the contaminated soil to a remote toxic waste site is necessary. In other situations, on-site decontamination (detoxification) of the soil is possible and, if so, is ordinarily much less costly than trucking the soil to a toxic waste site. In cases in which the soil contamination is essentially non-halogenated hydrocarbons, which is frequently the situation, it is often possible to decontaminate the affected soil by heating (retorting) the soil to a temperature of several hundred degrees .degree.F. in the presence of air to decompose the hydrocarbon contaminants into carbon dioxide and water (steam) and ash.
For purposes of decontaminating soil, special high temperature soil treating apparatus may be provided. However, it is apparent that even relatively small volumetric spills of such hydrocarbon materials as oil may contaminate comparatively large amounts of earth, especially if the spill has had time to seep into the earth. Because, therefore, of the usually large volumes of earth to be treated and the high temperature to which the soil must be subjected in order to completely decompose the hydrocarbon contaminants, efficient operation of the soil decontamination apparatus is very important. Otherwise, the size of the equipment and the amount of fuel consumed thereby to generate the high temperatures may make contamination clean up so expensive that many spillage accidents will be unreported and/or may ineffectively be covered up with layers of earth to hide the fact that a spillage has occurred. Also, excessively costly decontamination processes may render bankrupt some companies that are responsible for contaminating spills and the costs of decontamination may then fall upon the tax-paying public. In still other cases, high decontamination costs may lead to illegal dumping of contaminated soil, often in otherwise "sanitary" land fills, and may accordingly result in future water supply and public health problems.
There is disclosed in U.S. Pat. No. 3,745,700 to Hahn, a transportable soil drying machine which employs a conventional, aircraft-type jet engine to provide heat to and cause fluidizing of wet soil. The stated purpose of the machine is to dry soil that is otherwise tooo wet for such construction projects as earthen dams, roadways, and airport runways, thereby avoiding costly construction delays caused by wet weather and extending construction projects later into the fall and enabling earlier spring starting. Theoretically, equipment such as is disclosed by Hahn could possibly be used for decontamination of hydrocarbon-contaminated soil; however, the present inventor considers that the use of the jet engines for this purpose would not only be excessively expensive in terms of fuel consumed by the engines, but would also be relatively ineffectual at achieving complete soil decontamination and could cause other problems such as air pollution.
Various types of infrared and/or radiant heating apparatus have been described, for example, in U.S. Pat. No. 2,675,905 to Placek; U.S. Pat. No. 2,895,544 to Parsons;
U.S. Pat. No. 4,295,826 to Vasilantone; and U.S. Pat. No. 3,248,099 to Bratko. The Placek patent discloses an infrared heater for heating metal parts for stress relief after welding, or for heat treating and the like. Parsons and Bratko disclose radiating wall furnaces and Vacilantone discloses an infrared dryer for freshly painted products. While these cited patents generally disclose the use of high temperature heating apparatus, none disclose how the heating process might be applied to the specific problems relating to economical and effective decontamination of large volumes hydrocarbon polluted soil.
It is, therefore, an object of the present invention to provide novel apparatus for the decontamination of hydrocarbon-contaminated earth.
Another object of the present invention is to provide novel apparatus for decontaminating hydrocarbon-contaminated earth in a sealed, negative pressurized furnace, which utilizes heat radiation in the near-infrared region to vaporize and incinerate the hydrocarbon contaminants.
Still another object of the present invention is to provide novel apparatus for decontaminating hydrocarbon-contaminated earth which is truly mobile and which can readily be transported from one contamination site to another.
Other objects, advantages and features of the present invention will become apparent to those skilled in the art from the following detailed description taken in conjunction with the accompanying drawings.